Tesla Steps Up Production

[c1ue]

Re: Tesla Steps Up Production

The potential issues with electric cars are not in the beginning, they will crop up later.

How well will the battery banks hold up over time?

If the Volt's present range is 100 miles (electric only), then a 25% degradation has serious consequences.

Gasoline engines don't have this problem.

Hybrids, on the other hand, have the combination of being always able to drive as well as optimizing the use of the battery. Unfortunately there is a weight penalty.

[santafe2]

Re: Tesla Steps Up Production

If the Volt's present range is 100 miles (electric only), then a 25% degradation has serious consequences.

Gasoline engines don't have this problem.

Hybrids, on the other hand, have the combination of being always able to drive as well as optimizing the use of the battery. Unfortunately there is a weight penalty.

You might be thinking of the Nissan Leaf. The Volt on an average day will only drive 40 miles on battery power but is powered by gasoline after that. The Volt is a non-traditional hybrid.

[c1ue]

Re: Tesla Steps Up Production

You might be thinking of the Nissan Leaf. The Volt on an average day will only drive 40 miles on battery power but is powered by gasoline after that. The Volt is a non-traditional hybrid.

Indeed.

Although one question I have is - if there's a small gasoline engine anyway, what exactly is the point of having a 2nd engine - only electrical?

I'd be curious to see what the actual weight vs. performance of a hybrid engine is vs. a traditional gasoline only engine - unless it is better, then the only real environmental benefit the hybrid is a stealth downsizing of engine size.

[GRG55]

Re: Tesla Steps Up Production

Indeed.

Although one question I have is - if there's a small gasoline engine anyway, what exactly is the point of having a 2nd engine - only electrical?

I'd be curious to see what the actual weight vs. performance of a hybrid engine is vs. a traditional gasoline only engine - unless it is better, then the only real environmental benefit the hybrid is a stealth downsizing of engine size.

This is not correct.

In fact over time the engine size in one of the most popular hybrids, the Toyota Prius, has increased from earlier versions, and is now a 1.8 litre four-banger. That's a full 300 cc bigger displacement than the first generation Prius engine and a full 300 cc bigger than my first car, a 1968 VW Beetle, which engine wasn't nearly as high an output per unit of displacement as the modern Toyota.

The reason the hybrid has better fuel economy than a similarly equipped gasoline engine-only car has to do with the unique characteristic of electrical motors that they can generate their maximum torque at zero RPM. It's much, much more energy efficient to get a mass (like a car) moving from a standstill using an electric motor than any Otto-cycle (spark ignition gasoline) engine or Diesel-cycle (compression ignition) engine. It's the reason railway engines have been "hybrid" diesel-electrics since inception. It's also the reason that hybrids shine in stop-go city traffic, and are no more efficient than a conventional vehicle for long-haul highway excursions (the gasoline engine runs all the time when continuous high output is required, such as overcoming the parasitic drag on a 3 hour trip at 70 mph).

The main reason for the increasing displacement of the Prius engine is that Toyota is using variable valve timing to simulate an Atkinson-cycle engine. An Atkinson-cycle engine is thermally more efficient than a conventional Otto-cycle engine, but suffers from a lower power density (output per unit of displacement)

[leegs]

Re: Tesla Steps Up Production

This is not correct.

In fact over time the engine size in one of the most popular hybrids, the Toyota Prius, has increased from earlier versions, and is now a 1.8 litre four-banger. That's a full 300 cc bigger displacement than the first generation Prius engine and a full 300 cc bigger than my first car, a 1968 VW Beetle, which engine wasn't nearly as high an output per unit of displacement as the modern Toyota.

The reason the hybrid has better fuel economy than a similarly equipped gasoline engine-only car has to do with the unique characteristic of electrical motors that they can generate their maximum torque at zero RPM. It's much, much more energy efficient to get a mass (like a car) moving from a standstill using an electric motor than any Otto-cycle (spark ignition gasoline) engine or Diesel-cycle (compression ignition) engine. It's the reason railway engines have been "hybrid" diesel-electrics since inception. It's also the reason that hybrids shine in stop-go city traffic, and are no more efficient than a conventional vehicle for long-haul highway excursions (the gasoline engine runs all the time when continuous high output is required, such as overcoming the parasitic drag on a 3 hour trip at 70 mph).

The main reason for the increasing displacement of the Prius engine is that Toyota is using variable valve timing to simulate an Atkinson-cycle engine. An Atkinson-cycle engine is thermally more efficient than a conventional Otto-cycle engine, but suffers from a lower power density (output per unit of displacement)

I question whether your explanation above for the increased economy is really the most important. I would have thought that regenerative braking, where the kinetic energy of the car is captured and put back into the batteries during deceleration / braking, is the main factor in the increased fuel economy during stop-and-go driving.

[GRG55]

Re: Tesla Steps Up Production

I question whether your explanation above for the increased economy is really the most important. I would have thought that regenerative braking, where the kinetic energy of the car is captured and put back into the batteries during deceleration / braking, is the main factor in the increased fuel economy during stop-and-go driving.

I don't think so.

Unless the vehicle is a plug-in hybrid (like the Volt) ALL of the energy to move the vehicle originates from the gasoline in the tank. I am most familiar with the conventional Prius hybrid (they also make a plug-in variant).

Each time energy is converted from one form to another there are losses. Think of the number of energy conversions required to get a hybrid vehicle like a Prius in motion in the first place - gasoline to mechanical work in the engine which drives the generator (MG-1 in a Prius), back to potential energy in the battery and then to mechanical work through the planetary gear transmission driven by the traction motor (MG-2 in a Prius). All of those mechanical and chemical conversions, including the transmission, have losses, and all of that has to happen before there is any kinetic energy (vehicle motion) to be "conserved" by the regenerative braking system.

The regenerative braking system works by momentarily converting the traction motor to a generator...the vehicle wheels drive the transmission which drives the traction motor which stores energy in the battery, and all that has to go through the same conversions (and associated losses) in reverse before it is available once again to the front wheels to move the vehicle. In addition the amount of kinetic energy that can be recaptured is limited by the maximum charge rate and the available charge headroom of the battery pack. In the case of the Prius the high-voltage battery pack isn't very large so the car has two other braking modes...first compression braking through the transmission/MG-1/combustion engine (it's called B-mode) and then the conventional friction brakes front and back. Neither of these can "recover" any useful energy. When it's all put together, regen braking can only capture a minor fraction of the gasoline sourced energy that was used to get the vehicle in motion in the first place. It certainly helps improve vehicle efficiency but its not the main reason hybrids outperform conventional vehicles under stop and go conditions. The high torque at zero RPM is the reason the Prius always uses the electric traction motor for a standing start.

[leegs]

Re: Tesla Steps Up Production

Thanks for the explanation. I have wondered how much braking energy is captured via the regen process before regular brakes (or compression braking) kick in.

However I'm still not clear on why the max torque at zero RPM makes the electric motor more EFFICIENT. It's clear that it makes it more effective for getting the car going.

We can consider the amount of work that the engine must do to get the car up to speed (call it W(A) for work(acceleration)), and we could also consider the amount of work it has to do to maintain some steady speed for some period of time (W(S) - work(steady speed). I guess you're saying that the gasoline engine will burn relatively more fuel to deliver let's say 200 kJ during acceleration, that it would to deliver the same 200 kJ during steady state motoring. This makes sense as it's generally running at a higher RPM during acceleration, the transmission is slipping more, etc. On the other hand presumably the electric motor uses similar amount of juice to deliver the same useful work, whether during acceleration or during steady state use.

Having thought through this, I'm more convinced. Still surprised that this factor is more important than regenerative braking, but I'll take your word for it!

[GRG55]

Re: Tesla Steps Up Production

Thanks for the explanation. I have wondered how much braking energy is captured via the regen process before regular brakes (or compression braking) kick in.

However I'm still not clear on why the max torque at zero RPM makes the electric motor more EFFICIENT. It's clear that it makes it more effective for getting the car going.

We can consider the amount of work that the engine must do to get the car up to speed (call it W(A) for work(acceleration)), and we could also consider the amount of work it has to do to maintain some steady speed for some period of time (W(S) - work(steady speed). I guess you're saying that the gasoline engine will burn relatively more fuel to deliver let's say 200 kJ during acceleration, that it would to deliver the same 200 kJ during steady state motoring. This makes sense as it's generally running at a higher RPM during acceleration, the transmission is slipping more, etc. On the other hand presumably the electric motor uses similar amount of juice to deliver the same useful work, whether during acceleration or during steady state use.

Having thought through this, I'm more convinced. Still surprised that this factor is more important than regenerative braking, but I'll take your word for it!

The torque from a gasoline engine running at low speed is very low. Even before the vehicle is moving the gasoline engine has to be running (idle speed) which uses energy. Most gasoline engines do not generate enough torque to move the vehicle from a standing start at idle speed (release the clutch on a manual transmission car without touching the accelerator pedal and under almost all circumstance the engine will quit). To overcome this means increasing engine RPM (and therefore output torque) and fuel consumption rate before connecting to the drive wheels through the transmission (again, notice how a manual transmission vehicle is put into motion by coordinated manipulation of the accelerator and clutch pedals...in an automatic transmission car the torque converter does the same thing as you do with a manual clutch). A hybrid's electric motor uses no energy when the car is stationary and since the motor produces maximum torque just as it starts to rotate it can be direct connected to the axle with no energy loss creating clutch, torque converter or transmission in between. For example, in the Prius the traction motor is direct coupled to the drive axle reduction gearing through the ring gear of the planetary "power split device" transmission (which is what Toyota uses to mechanically connect the electric motor and gasoline engine drive sources).

As a conventional gasoline engine vehicle accelerates from a standing start the engine RPM increases, and then almost immediately has to be allowed to fall off again to shift to second gear, and the process is repeated. A gasoline engine is hopelessly inefficient at this particular task. The hybrid systems try to keep the gasoline engine running only within its most efficient speed range, typically about 1500 RPM to 4500 RPM, no more, no less. In the Toyota the gasoline engine shuts down completely (if not needed to charge the high voltage battery) for standing start acceleration or slow speed operation (affectionately known as stealth mode according to my formerly "green" friends - every Prius owner I know personally has moved back to a conventional vehicle ). At moderate speeds, where most of the work is needed to overcome parasitic drag and not to dv/dt (accelerate) the vehicle, the gasoline engine does all the work of propelling the vehicle and charging the high voltage battery if needed. That is why in the early marketing stages people who had a relatively uninterrupted commute to work sensed that the Prius fuel mileage wasn't all that much greater than a similar conventional car.

If you do a lot of long distance driving on the Interstates or in low population rural States (hello Wyoming) a hybrid is a complete waste of money. If you do a lot of urban stop and go driving, getting to modest speeds in between, the hybrid is really in its element...especially in a moderate climate where you don't need to use the air conditioner or heater a lot.

Hope this helps...

[shiny!]

Re: Tesla Steps Up Production

If you do a lot of long distance driving on the Interstates or in low population rural States (hello Wyoming) a hybrid is a complete waste of money. If you do a lot of urban stop and go driving, getting to modest speeds in between, the hybrid is really in its element...especially in a moderate climate where you don't need to use the air conditioner or heater a lot.

Very interesting stuff. Most of the taxi cabs in my city have switched to Prius. That kind of stop and go city driving is perfect for a hybrid. For my long commute on the highway I'm glad I didn't spend the extra bucks for one. I'd have never recouped the money on gasoline savings.

BTW and unrelated: Y'all have heard me grouse about my Hyundai Accent and how much I miss my grand old Crown Vic. Yesterday a woman pulled out of a driveway right in front of me when I was going about 35. I hit my brakes and swerved slightly to go behind her, expecting her to keep going. But she froze and stopped dead in front of me. I had to slam my brakes HARD. Came to a stop about 3 inches from broadsiding her, without skidding. The Crown Vic could never have stopped in that short a distance. The 2012 Accent has FANTASTIC brakes.

Of course, if I had clobbered her, the Crown Vic could have driven away while the Accent would have been totalled...

[c1ue]

Re: Tesla Steps Up Production

This is not correct.

In fact over time the engine size in one of the most popular hybrids, the Toyota Prius, has increased from earlier versions, and is now a 1.8 litre four-banger. That's a full 300 cc bigger displacement than the first generation Prius engine and a full 300 cc bigger than my first car, a 1968 VW Beetle, which engine wasn't nearly as high an output per unit of displacement as the modern Toyota.

This itself isn't meaningful - the exact same trend exists for gasoline engine car lines.

Don't you remember the first Honda Accord vs. what is sold today?

More importantly, what is the size of a top of the line Prius' engine vs. an equivalent Toyota top of the line mass- or mid- market gasoline vehicle?

According to this - the V6 Accord is 3.4 Liters. Quite a bit larger than 1.8, no?

The reason the hybrid has better fuel economy than a similarly equipped gasoline engine-only car has to do with the unique characteristic of electrical motors that they can generate their maximum torque at zero RPM. It's much, much more energy efficient to get a mass (like a car) moving from a standstill using an electric motor than any Otto-cycle (spark ignition gasoline) engine or Diesel-cycle (compression ignition) engine. It's the reason railway engines have been "hybrid" diesel-electrics since inception. It's also the reason that hybrids shine in stop-go city traffic, and are no more efficient than a conventional vehicle for long-haul highway excursions (the gasoline engine runs all the time when continuous high output is required, such as overcoming the parasitic drag on a 3 hour trip at 70 mph).

The main reason for the increasing displacement of the Prius engine is that Toyota is using variable valve timing to simulate an Atkinson-cycle engine. An Atkinson-cycle engine is thermally more efficient than a conventional Otto-cycle engine, but suffers from a lower power density (output per unit of displacement)

I don't disagree that the electric motors have better starting torque, however, this isn't the only factor.

What is the relative impact of the greater weight introduced by the combination of electric + gasoline motors, regenerative braking, and battery packs?

Hence my previous question. If an electric motor + battery pack + regenerative braking system + 1.8L gasoline motor outperforms an otherwise identical car with just a 1.8L gasoline motor, then it is fair to say there are fundamental benefits.

Comparing an electric motor + battery pack + regenerative braking system + 1.8L gasoline motor vs. a 2.4 liter (standard Accord) engine isn't an apples to apples comparison - even if the hybrids are almost certainly incorporating different materials in an attempt to try and reduce overall weight.

[GRG55]

Re: Tesla Steps Up Production

This itself isn't meaningful - the exact same trend exists for gasoline engine car lines.

...

Evidently I completely misunderstood you:

Indeed.


Although one question I have is - if there's a small gasoline engine anyway, what exactly is the point of having a 2nd engine - only electrical?


I'd be curious to see what the actual weight vs. performance of a hybrid engine is vs. a traditional gasoline only engine - unless it is better, then the only real environmental benefit the hybrid is a stealth downsizing of engine size.

[santafe2]

Re: Tesla Steps Up Production

Indeed.

Although one question I have is - if there's a small gasoline engine anyway, what exactly is the point of having a 2nd engine - only electrical?

I can only speak personally about this since I live in a small town and seldom drive more than the 40 miles the Volt allows on electricity. The other engine isn't traditional, it's more like a generator. When it turns on it sounds like a bad 2-stroke lawn mower. It charges the batteries and turns off for several miles. If I could buy a Volt that went 100 miles like the Nissan Leaf but still had the Volt gasoline backup, that would be a nearly perfect car. We added 2,500 watts of solar on our house to support the Volt. I hope all this matters but you can never be sure.

[reggie]

Re: Tesla Steps Up Production

The original run on the $109,000 Roadster was 2,500. The Model S is planned for an initial production run of 5,000, increasing to 20,000 by 2013. Pricing is $54,400 to $77,400, depending on battery capacity.

Details should be available online in a few days at SFGate.

Is this vehicle on the road yet, as everyday I walk past a black Tesla sedan that looks identical to the one in this photo. I gotta say, I'd love to test drive one.

[GRG55]

Re: Tesla Steps Up Production

Is this vehicle on the road yet, as everyday I walk past a black Tesla sedan that looks identical to the one in this photo. I gotta say, I'd love to test drive one.

Sure is... http://www.teslamotors.com/models

Base price $62,400 after the $7500 US Federal rebate (your tax dollars at work)
Higher capacity battery model base price $72,400
Performance model $87,400 (Musk really has a thing for prices ending in 400)

Metallic paint $750 (otherwise available only in Henry Ford black and virgin white)
Pearl clear coat paint $1500
Glass roof $1500
High performance tires on 21" wheels $3500 (on all versions, including the "performance version"...go figure)
Performance Plus suspension package $6500 (only available as an option on the "performance version"...go figure)
Tech Package $3750; back up camera, memory seats, nav system, Xenon headlights, keyless entry... (No point having a high tech car without the tech package, eh)

And don't forget the $1500 High Power Wall Connector, which is described thus:
"The High Power Wall Connector is designed to complement the fluid, futuristic design aesthetic of the car it plugs into. Install this work of art in your garage or parking area with a power supply of up to 20 kW. With 20 kW of power, a Model S equipped with Twin Chargers can recover 62 miles of range per hour of charging."

The car looks great just standing still, and being electric it should be a rocket as a stop-light racer.

[Polish_Silver]

GAs engine size in hybrids

This is not correct.

In fact over time the engine size in one of the most popular hybrids, the Toyota Prius, has increased from earlier versions, and is now a 1.8 litre four-banger. That's a full 300 cc bigger displacement than the first generation Prius engine and a full 300 cc bigger than my first car, a 1968 VW Beetle, which engine wasn't nearly as high an output per unit of displacement as the modern Toyota.

The reason the hybrid has better fuel economy than a similarly equipped gasoline engine-only car has to do with the unique characteristic of electrical motors that they can generate their maximum torque at zero RPM. It's much, much more energy efficient to get a mass (like a car) moving from a standstill using an electric motor than any Otto-cycle (spark ignition gasoline) engine or Diesel-cycle (compression ignition) engine. It's the reason railway engines have been "hybrid" diesel-electrics since inception. It's also the reason that hybrids shine in stop-go city traffic, and are no more efficient than a conventional vehicle for long-haul highway excursions (the gasoline engine runs all the time when continuous high output is required, such as overcoming the parasitic drag on a 3 hour trip at 70 mph).

The main reason for the increasing displacement of the Prius engine is that Toyota is using variable valve timing to simulate an Atkinson-cycle engine. An Atkinson-cycle engine is thermally more efficient than a conventional Otto-cycle engine, but suffers from a lower power density (output per unit of displacement)

When hybrids were first introduced, the rationale I heard was this:

In conventional cars, the full power of the gas engine is rarely used. It is needed for steep hills and passing, but 95% of the time the engine is running at 30% of it's rated power. This is inefficient. The hybrid was supposed to use a smaller engine, which, when on, would be at 70% of it's capacity. The electrical system would provide the needed power surge. By running a smaller engine at higher capacity, and over more narrow range of RPM, the efficiency is higher.

I have no numbers to know if this actually works in practice.